The present invention relates to interrupt control techniques making use of a local time timer included in a semiconductor data processing device applied to a terminal coupled to a network for time-triggered communication in which communication is performed in synchronization with a common time used in the network and also relates to techniques related with time-triggered communication systems effectively applicable to, for example, communication systems included in electronic control devices for automobiles.
In communication systems in which frames are exchanged between plural terminals via a transmission path, particularly, communication systems for communications between electronic control devices applied to, for example, vehicle-mounted devices or factory production lines, time trigger systems to control, based on time, the timing of, for example, frame transmission/reception or setting changes are used. For example, techniques based on FlexRay (registered trademark) are applied to vehicle-mounted networks used as time trigger systems. In such systems, to integrate a terminal into a network, time synchronization based on a common time used in the network (referred to as a “global time”) is established as described in “Flex Ray Communication System Protocol Specification Ver. 2.1 Rev. A (15 Dec. 2005).” The time synchronization is established using the time when a frame called a start-up frame transmitted from at least one terminal already integrated in the network is received by the terminal to be integrated into the network and the expected arrival time of the start-up frame calculated based on a communication schedule by the terminal to be integrated into the network.
With such time synchronization established, transmission/reception processing based on a predetermined time schedule is enabled between terminals. To be concrete, a time-triggered communication protocol requires the terminals coupled to a network to perform communication while maintaining network time synchronization between them. For this, each terminal uses a local time timer which operates based on its own network time. When a local time set on a local time timer is reached, the local time timer issues an interrupt request to a CPU. Responding to the interrupt request, the CPU writes a transmit message to a RAM or reads a receive message from a reception buffer. In this way, transmission/reception processing based on a time schedule is enabled. Namely, the timing of transmission/reception processing is defined by a local time set on the local time timer. Thus, terminals to operate in time-triggered communication are required to synchronize, in real time, their local times with a global time. Therefore, it is not appropriate to use a general-purpose timer included in a microcomputer as a local time timer.
Applying the timer interrupt control technique disclosed in Japanese Unexamined Patent Publication No. 2011-76584 to the above interrupt control performed using a local time timer allows an interrupt control circuit to give an interrupt signal accompanied by a corresponding cause of interrupt to a CPU. This reduces the processing to be performed by the CPU to acquire interrupt cause data.